On 05/04/2019 18:46, Lew Pitcher wrote:
> Gareth's was W7 now W10 Downstairs Computer wrote:
>
>> Presumably the graphics controller fills up a frame buffer for display,
>> so, if one is not at a certain point using the controller to draw
>> something, could one write to the frame buffer directly?
>
> According to various official blogs, etc, yes. AIUI, the standard linux
> framebuffer api works properly on the Rpi.
>
>> Also, AIUI, the RPi communicates with the GPU via memory-based
>> message buffers, so the GPU must be running some form of background
>> kernel?
>
> Apparently, the GPU runs it's own microcode, which implements the
> "VideoCore" architecture. You can find detailed documentation on this
> architecture, and Broadcom's implementations for the RPi SoCs by searching
> the fine web.
>
>> I assume that this must be the purpose of only one of the GPU
>> processors as running full motion video, say, in an MPEG stream,
>> must take quite a lot of computer time?
>
> Of course.
>
>> One part of the GPU must be simply concerned with taking the frame
>> buffer and emitting it as a composite video stream, so I wonder how
>> the aspect ratio is set up?
>
> I'm not familiar with the internals of the VideoCore GPU, so I can't answer
> this question. Perhaps a thorough read-through of the VideoCore 3D
> Architecture Reference Guide would answer this question for you. See
>    https://docs.broadcom.com/docs/12358545
> for details.
>
>> Sorry, a bit unstructured in the above, just musing; it's something
>> that I pick up after a few months before dropping it again; I'm
>> struggling  to get to grips with the whole GPU thing.
>
> HTH
>

Have you looked at OMXPlayer? https://elinux.org/Omxplayer

Omxplayer is a video player specifically made for the Raspberry Pi's GPU
made by Edgar (gimli) Hucek from the XBMC/Kodi project. It relies on the
OpenMAX hardware acceleration API, which is the Broadcom's VideoCore
officially supported API for GPU video/audio processing.

Also here: https://github.com/popcornmix/omxplayer



--

Chris Elvidge, England

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